The eight month campaign in Gallipoli was fought by Commonwealth and French forces in an attempt to force Turkey out of the war, to relieve the deadlock of the Western Front in France and Belgium, and to open a supply route to Russia through the Dardanelles and the Black Sea. The Allies landed on the peninsula on 25-26 April 1915; the 29th Division at Cape Helles in the south and the Australian and New Zealand Corps north of Gaba Tepe on the west coast, an area soon known as Anzac. On 6 August, further landings were made at Suvla, just north of Anzac, and the climax of the campaign came in early August when simultaneous assaults were launched on all three fronts. However, the difficult terrain and stiff Turkish resistance soon led to the stalemate of trench warfare. From the end of August, no further serious action was fought and the lines remained unchanged.

The situation was complicated by the entry of Bulgaria into the war on the side of the Central Powers. On 5 October 1915 the British opened a second Mediterranean front at Salonika which would compete for reinforcements with Gallipoli. Also Germany would now have a direct land route to the Ottoman Empire, enabling it to supply heavy siege artillery which would be able to devastate the Allied trench network, especially on the confined front at Anzac. Having reviewed the state of his command, Monro recommended evacuation. Kitchener disliked the notion of evacuating the peninsula and made a personal visit to consult with the commanders of the three corps; VIII Corps at Helles, IX Corps at Suvla and Anzac. The decision to evacuate was made.

Evacuation of 14 divisions in winter in proximity to the enemy would be difficult and heavy losses were expected. The untenable nature of the Allied position was made apparent when a heavy rainstorm struck on 27 November 1915 and lasted for three days, followed by a blizzard at Suvla in early December. The rain flooded trenches, drowning soldiers and washing unburied corpses into the lines. The following snow killed yet more men from exposure. Ironically the evacuation was the greatest Allied success of the campaign. Suvla and Anzac were to be evacuated in late December, the last troops leaving before dawn on 20 December 1915. Troop numbers had been progressively reduced since 7 December 1915 and cunning ruses, such as William Scurry's self-firing rifle (described below), were used to fool the Ottomans and prevent them discovering that the Allies were departing. At Anzac, the troops would maintain utter silence for an hour or more until the curious Ottomans would venture out to inspect the trenches, whereupon the Anzacs would open fire. As the numbers in the trenches were thinned, rifles were rigged to fire by water dripped into a pan attached to the trigger. The entire Allied force was evacuated, but large quantities of supplies and stores fell into Ottoman hands.[36] Helles was retained in case the British wanted to resume the offensive. However, a decision to evacuate there also was made on 27 December. The Ottomans were now warned of the likelihood of evacuation and mounted an attack on 6 January 1916 but were repulsed. The last British troops departed from Lancashire Landing on 9 January 1916. Amazingly, only two soldiers were wounded during the evacuation, despite the prior warnings of 50% casualties from Sir Ian Hamilton.